As discussed in the text, pathologic Q waves may be a marker of transmural infarction. Notice that the left ventricle consists of an outer layer (epicardium) and an inner layer (subendocardium). This distinction is important because myocardial ischemia may be limited to just the inner layer, or it may affect virtually the entire thickness of the ventricular wall (transmural ischemia).įIGURE 8-1 Cross section of the left ventricle showing the difference between a subendocardial infarct, which involves the inner half of the ventricular wall, and a transmural infarct, which involves the full thickness (or almost the full thickness) of the wall. Right ventricular infarction is also discussed briefly.Ī cross-sectional diagram of the left ventricle is presented in Figure 8-1 . This discussion focuses primarily on ischemia and infarction of the left ventricle, the predominant chamber of the heart. Myocardial infarction (MI) refers to myocardial necrosis (“heart attack”), which is usually caused by severe ischemia. If the ischemia is more severe, necrosis of a portion of heart muscle may occur. For example, patients who experience angina pectoris with exercise are having transient myocardial ischemia. Myocardial ischemia may occur transiently. Ischemia means literally to hold back blood. If severe narrowing or complete blockage of a coronary artery causes the blood flow to become inadequate, ischemia of the heart muscle develops. Oxygenated blood is supplied by the coronary arteries. Myocardial cells require oxygen and nutrients to function. This chapter and the next examine one of the most important topics of clinical electrocardiography: the diagnosis of myocardial ischemia and infarction (ischemic heart disease). Section I ST segment elevation ischemia and Q wave infarct patterns
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